Manufacture of rubber products



vulcanized by sulfur.

Patented Jan. 18, 1949 MANUFACTURE or Runners rrtonnc'rs Mark M. Heywood,- Twibkenhanr, l lnglandas signor to The pany, Akron,-v Qhio, a

No Drawing. Applicati rial No. 786,329. In Greait't:

Firestone Tire, & Rubber Chm-r corporation of Ohio on November 15, 1947', Se-

Britain; March 26,

Section 1,. Public Law 690', Xirg'ust' 8;;1946

. l invention relates to the" manufacture of rubber products, and it relates more particularly to the vulcanization of rubber and synthetic rubber' compositions and articles comprising the same. This application is a continuation-in-part of my copending aplication Serial No. 551,427, filed August 26, 1944, now abandoned;-

The chief objects'of the invention, are-tos'peed up andimprove the action of thethiazole-typeof rubber vulcanization acceleratorsto provide; vulcani'zed natural and synthetic rubbery composi= tibns of improvedpliysical propertieaand to pro-- vide a commercially practical method of'vul'can izing rubbery articles by theuse of much smaller proportions of accelerator than are commonly used; Other" obj ects-will' be' readily apparent in the description of the invention which follows.

The objects of the-invention are: realized by" adding to thervulcanizable' rubbery composition; an addition compound of cyclohexyl'amine o1"di-' cyclohexylamine' and a cresol or a hydrocarbon substituted cr'esol. Examples of suitable creisol". derivatives are' 0-, m and.- p -cresol, homologs of cresols, such as the xylenols; t-butylphenol', oc'ftylphenol; decylphenol, and other hydrocarbone substituted cresols. such as'benzylatedcresols and the'like. Although theseaddition compounds, or substituted ammonium salts; are not very effective vulcanization accelerators when used alone, they substantially intensify the accelerating activity ofi thiazole type accelerators.

Suitable accelerators conform to the generar formula Tz D, wherein Tz represents, atm'azyr radical and D represents a. mercapt ol on substit i'itd mercapto radical of me-g oup; ST-I, -S'STz, -'-SNR2, and SH-NR";; it beingqund'erstood that-R may represent hydno'gen-or aih ydriocarbon substituent. Examples are mercapitobenzothia'zol'e, ethylthiazylmercap't'an', dimethyl thiazyl'mercaptan the amine salts disulfides and sulfenamide derivatives. thereof. f

The invention is applicable to= all. natural and synthetic: rubbery compositions which may be These include natural rub- Table 1 by I Weight Ingredients Control J Test Rubbery copolymer of butadiene and styrene 100 100 Stearic acid 2. 5 2. 5 Pineztar i 2.6 2. 6 Zinc oxide.- 2. 4 2. .4 Carbon black. 45. 0 4510 Antioxidant 0L6 0:65, Su1 fur 1.7; 1.7. COM-ta!dlStlllEteSOftGnei': 4; U 4; 0' Neyclohexylfg benzcthiazyl s en 1.2 0,9? Oyclohexylammonium cresylate 2,9

15 claims (01.v zed-19).

2 be'r,-. reclaimed rubber, polyis'oprefiegpol y'but'adien'e; cop olymers ot"l,3-butadi'ene=with styrene or acryloni trile, and other vulcanizable rubbery olymers of two or more monomers; one or whichis a conjugated diolefin.

The addition compounds of the invention may be used. in various proportions, e. g., from 0.1 to. 5.0 parts per 100 parts of rubber. The thiazoletypeaccelerator may be employed in the same range of proportions, but less of the accelerator than usuai iseniployed with increasing proportions of the" cycloheXylamine-cresol addition compound.

The invention issfurther disclosed in the followe ihig 'examples, in which allparts areby weigh't;

EXAMPLE 1 Cyclohexylanimonium cresylate was? prepared? by mixing: equimole'cular quantitieszof cyclohexyl fenamide;.-i'n a commercial rubbery copolymer of 1,3-butadiene and styrene; Accordingly, control and test: compositions were mixed in conformity with Tablei.

by heating at 20, 40, 60 and 160 minutes at 280 F., and modulus and tensile data were obtained on the vulcanizates, as set out in Table 2.

Table 2 Mogulhuslgf alas T n th tici y s. in. ens strong in Vulcamzed Composition at elongation of lbs.,in. at break Cure in minutes 40 80 160 20 40 80 160 0 trol 450 850 980 250 2, 150 2, 850 2, 750 900 825 2, 425 2, 950 2, 980 2, 800

Test 725 One of the disadvantages of vulcanized rubbery copolymers of butadiene and styrene is that if a cut is made in a vulcanized block of the vulcanized copolymer and the H cut is subjected to flexing, the out increases in length much more quicklythan would be the case with natural rubber. However, the inclusion of a cyclohexylammonium cresylate or a dicyclohexylammonium cresylate in the copolymer prior to vulcanization reduces thepropensity of the vulcanizate to out growth, as will be apparent from an examination of Table 3, wherein there are shown results of flexing tests carried out on blocks of the two compositions mixed in accordance with Table 1; each test block was provided with a slit 0.1 inch deep and 0.2 inch long; the slit test blocks were flexed for one hour.

Table 3 Increase in lengh of it at end of test 80 minutes 80 minutes at 280 F. at 298 F.

Cure of test blocks Inches Control composition 102 0. 081

Test composition Control composition: Time, 18 minutes to decomposition.

Test composition: Time, 21 minutes to decomposition. 1

EXAMPLE 2- An additional quantity of cyclohexylammonium cresylate was prepared by adding 184.3 grams of eyclohexylamine to 201 grams of commercial mixed cresols (mole/mole) with constant stirring and cooling in an ice bath. The additionwas carried out over a period of one and one-half hours at a temperature of 15 to 20 C. The yield was 281 grams-of a wine colored liquid.

area containing the Table 4 Formulas Control Test Butadienestyrene copolymer 100 Asphalt plasticizer. 10 10 Carbon Black 50 50 no oxide 5 5 ulfur 2. 5 2. 5 N-cyclohexylQ-benzothiazyl sulf 0. 75 0.25 Cyelohexylammonium cresylatc 2. 0

Total 168. 25 169. 75 Modulus at 300% in lbs/ink:

Cured 20 min. at 280 F 975 975 Cured 40 min. at 280 F 1,175 1, 050 Cured 80 min. at 280 F 1, 250 l, Cured min. at 280 F 1, 225 1,150 Tensile strength in lbs/in]:

Cured 20 min. at 280 F... 2, 200 Cured 40 mins. at 280 F 1, 875 Cured 80 min. at 280 F. .1, 875 Cured 160 min. at 280 F 2,100

FLEXOMETER BLOWOUT TESTTEST BLOCKS CURED 80 MIN. AT 280 F.

Minutes to decomposition; 29 48 Cut growth resistance-relatiw: v Blocks cured 80 min. at 280 F 100 217 Blocks cured 80 min. at 298 F 112 168 1 Flexometer disclosed in U. S. Pat. 2,048,314. Test block is placed on revolvable plate under a load of 550 pounds. Plate is ofi-set 0.4 inch from center and revolved rapidly until block is deflected or compressed 0.3 inch below original height under the load, at which time block is considered decomposed or blown out.

EXAMPLE 3 The activator of Example 2was tested with the thiazole-type accelerator, the eyclohexylamine salt 'of mercaptobenz'othiazole, in the butadienestyrene copolymer. test formula used in Example 2. As a sort of control composition, the test composition of Example 2 was employedand is herein referred to as Test composition2. The Test composition 3 cal with Test composition 2 excepting in the weight-for-weight replacement of the sulfenamide by the eyclohexylamine salt of mercaptobenzothiazole. Test results are given in Table 5.

Table 5 Test Cam Test Composition 2 v position 3 We... at 00% in lbs./in. Cured 20 min. at 280 F 725 .775 Cured 40 min. at 280 F.. 1, 100 1, 200. Cured 80 min. at 280 F.. 1, 225 1, 300 Cured 160 min. at 280 F l, 650 l, 525 Tensile strength in Illa/in 4 Cured 20 min. at 280 F 1, 775 r 1, 600 Cured 40 min. at 280 F.. 2, 275 1,650- Cured 80 min. at 2809 F 1, 650 .1, 600. Cured 160 min. at 280 F 2, 1, 715

1 FLEXOMET ER BLOW-our T E'sr. f Minutes to decoinposition..'

of this'example was identi theiormulasof Table 6, wherein thev normal iphysicalltesting data are presented.

Table 6 1;; Formulas 4 Control Test Natural rubber. 100 100i Suliurm- 6. 6E (i Zinc oxide 11.4 '11. 4 Sterric acid p 1.9 1.9 Mercaptobenzothiazole 0. 95v 0. 95 Cyclohexylammonium cresylete 0. 12 Total 120. 90 121. 02

Modulus in lbs/in. at 600%: ure 30 min. at 804 1,300 Cured 60 min. at 260 F..- 1, 072 1, 237 Cured 90 at 260 F 1, 050 1,050 Tensile strength in lbs/in}: Cured 30 at 260 F- 3, 630 Cured 60 min. at 260 F- 3, 290 Cured 90 min. at260 F- 3, 003 Percent elongation at break: Cured 30 min. at 260 F 771 Cured 60 min at 260 F--- 759 Cured 90 min. at 260 F 767 750 I EXAMPLES Table 7 Formula Control Test Rubber 100 100 Carbon black. 49. 0 49. 0 Zinc oxide 3.0 3.0 Stearic acid 3. 0 3.0 Liquid plasticizer 4. 0 4. O Antioxidant 2.0 2. 0 Sulfur 2. 2. 25 N-cyclohexyl-2-benzothiazyl sull' 1. 0 1. 0 Cyclohexylammonium cresylate 0. 25 104. 25 164. 50

Modulus in lbs/in. at 300%:

Cured 10 min. at 280 F 817 Cured 15 min. at 280 F-- 957 Cured min. at 280 F-. l, 585 Cured min. at 280 F 1, 592 Tensile strength in lbs./in.'-:

Cured 10 min. at280 F 4, 430 Cured 15 min. at 280 F... 623 4, 613 Cured 30 min. at 280 F-- 4, 537 3, 900 Cured 45 min. at 280 F 4, 087 3, 657

Durometer hardness (test piece cured 15 min. at 280 F.)

Control Test EXAMPLE 6 Table Formula. Control Test Butadiene-styrene copolymer..- 100 Stearic ac 2. 5 Coal tar distilla 4. 0 Petroleum distillate residue 2. 6 Antioxi nt... 0. 6 Carbon black. 45. 0 Zine oxide-.- 2 4 Sulfur 1.7 Dibenzothiazyl disulflde. l. 6 Cyelohexylammomum cresyle e..... 2.0

Total 160. 4 Y 162. 4

Modulus in lbs/in. at 400%:

Cured 20 min. at 280 F- 1, 35 0 .Oured 40min. at 28 1, 7 0 Cured min. at 280 F. v 2,025. Cured 160 min. at280 F.. 2, 025 Tensllestreugtlr m lbs/in Cured 20. mm M20091 2, 525 3,125 Cured) min at 280 2, 425 2, 350 Cured 80 min at'280 F. 2, 425, Cured 160 min. 2 2,125

mam 7.

accelerated by a thiazyl mercaptan, in accordance with Table 9.

Table 9 Formula Control Test -l3utadiene-styrene copolymer. 10 Steeric acid 2- 5 2- Coal tar distillate. 4. 0 4. Petroleum distillat 2. 6 2. Antioxidant 0.6 0. Garbonblac 45. 0 45. Zinooxide I 2. 4 2.

1. S. m 1.7 '1. Mercaptobenzothiazola-..., 1. 0. l. Cyclohexylammonium cresylate 2;

V Total 160. 4. 16 2. Modulus in lbs/in. at 400%: i

Cured 20 min. at 280 100 1, 700

Cured 40 min. at 280 F- 350 2, 000

Cured 80 min. at 280 F. 950 2, 200

Cured min. at 280 F 1, 550 2, 300 Tensile strength in 1bS./ll1. Z

Cured 20 min. at 280 F- 200 2, 625

Cured 40 min. at 280 F- 1, 350 2, 450

Cured 80 min. at 280 F- 2, 400 2, 600

Cured 160 min. at 280 F 2, 600 2, 600

The above examples show the consistent activating efiect of the cyclohexylamine addition compound with cresol upon several commercial thiazole-type accelerators, in both natural and synthetic rubbers. The activator improves the aging resistance of both natural and synthetic rubber vulcanized in its presence, and it also allows a substantial reduction in the proportion of the relatively expensive thiazole-type accelerator, resulting in appreciable savings for equivalent performance of both natural and synthetic rubber compositions. The equivalent activators mentioned hereinabove, namely, the cyclohexylammonium salts of hydrocarbon substituted cresols and the dicyclohexylammonium salts of oresol or hydrocarbon substituted cresols, may be substituted for the preferred activator in the various examples with equivalent improved results.

It has been observed that large changes in the physical properties of vulcanizates result from slight variations in proportions of sulfur or accelerator, such that a variation of 0.1 part per 100 parts of rubber causes substantial changes in vulcanizate properties. In contrast, the proportion of the activator of the invention may be varied widely, as from 1.0 to 2.0 parts per 100 of rubber with only minor or unmeasurable difierences in physical properties of the vulcanizate. A possible explanation of this advantageous phenomenon is the fact that cyclohexylammonium cresylate is a solvent for sulfur, and thus an efllcient dispersant therefor.

What is claimed is: L a

1. Method of vulcanizing a substance of the group consisting of natural rubber, reclaimed .rubber and synthetic rubbery conjugated diolefin polymers, which includes heating the substance and sulfur in the presence of a thiazole accelerator and an activator of the class consisting of cyclohexylammonium and dicyclohexylammonium salts of a cresol. I v

2. Method of vulcanizing a substance of the group consisting of natural rubber, reclaimed rubber and synthetic rubberyconjugated diolefin polymers, which includes heating the substance and sulfur in the presence of a thiazyl mercaptan accelerator and cyclohexylammonium cresylate.

3. Method of vulcanizing a substance of the group consisting of natural rubber, reclaimed rubber and synthetic rubbery conjugated diolefin polymers, which includes heating the-substance and sulfur in the presence of a dithiazyl disulfide accelerator and cyclohexylammonium cresylate.

4. Method of vulcanizing a substance of the group consisting of natural rubber, reclaimed rubber and synthetic rubbery conjugated diolefin polymers, which includes heating the substance and sulfur'in the presence of a thiazyl sulfenamide accelerator andcyclohexylammonium ,cresylate.

5. A vulcanizable rubber, composition including a substance of the group, consisting of natural rubber, reclaimed rubber and synthetic rubbery conjugated diolefin polymers, sulfur, a thiazole accelerator and an activator of the class consisting of cyclohexylammonium and dicyclohexylammonium salts of a cresol. c

6. A vulcanizable rubber composition including a substance of the group consisting of natural rubber, reclaimed rubber and synthetic rubbery conjugateddiolefin polymers, sulfur, a thiazyl mercaptan accelerator and cyclohexylammonium cresylate.

7. A vulcanizable rubber composition including a substance of the group consisting of'natural rubber, reclaimed. rubber and synthetic rubbery conjugated diolefin polymers, sulfur, a dithiazyl disulfide accelerator and cyclohexylammonium cresylate.

8. A vulcanizable rubber composition including a substance of the group consisting of natural rubber, reclaimed rubber and synthetic rubbery conjugated diolefin polymers, sulfur, a' thiazyl sulfenamide accelerator and cyclohexylammonium cr'esylate.

9. Product of claim 1. '10. Product, of claim 2.

11. Product of claim 3.

12.- Product of claim 4. v

13. The method of making a vulcanizable composition, comprising mixing a rubbery copolymer of butadiene and styrene with sulfur, N-cyclohexyl-2-benzothiazyl sulfenamide and cyclohexylammonium cresylate.

14. A vulcanizable composition comprising a rubbery copolymer of butadiene and styrene, sulfur, N-cyclohexyl-Z -benzothiazyl sulfenamide and cyclohexylammonium cresylate.

15. A product produced by vulcanizing the vulcanizable composition claimed in claim 14.

MARK'M; rmywoon REFERENCES CITED The following referencesare of record in the file of this patent:

UNITED STATES PATENTS Number 

